Delay lines are routinely used in a wide variety of circuits and systems for the primary purpose of delaying the propagation rate of a signal, typically for timing reasons. Programmable delay lines are particularly useful in applications where the amount or duration of signal delay requires repeated adjustment.
In applications in which a high degree of control over the delay duration is required, it is important that the power supply voltage provided to the delay line be controlled so as to minimize voltage swing fluctuations. It is known, for example, that variations in the reference voltage supplied to a delay line can result in unintended alteration in the delay characteristics of the delay line. It is also known, by way of further example, that variations in power supply voltage provided to a delay line can induce unacceptable levels of skew and jitter in the signal propagated through the delay line. Signal discontinuities and perturbations may also be introduced during times in which the delay duration, or delay factor, of the delay line is being adjusted.
There exists a keenly felt need for a variable delay line that overcomes the above-noted deficiencies found in prior art delay line implementations, and one that is insensitive to fluctuations in power supply voltage. There exists a further need for a variable differential delay line that provides superior delay characteristics and control capabilities. The present invention fulfills these and other needs.